The present invention relates to a method for exposing an electron beam, and more particularly to a method for automatically correcting the size of the beam which tends to be deviated from its design size due to a change in position of an aperture for shaping the beam.
In order to shorten the time for patterning by an electron beam exposure, an electron-beam exposure apparatus of a beam-shaping type has already been proposed (see, for example, VL-S2, which was designed by Fujitsu LTD, et al., described in Nikkei Electronics, no. 235, pp 44-48). The apparatus of this type comprises a first aperture for shaping the cross section of an electron beam into a polygon or a rectangle, a second aperture having a shape of a polygon or a rectangle arranged so as to be able to cut a part of the electron beam shaped by the first aperture, and a deflection unit for deflecting the beam shaped by the first aperture, to a desired position on the second aperture. The electron-beam apparatus of this type can generate a rectangle of variable size on the surface of a sample or a semiconductor wafer. The size is varied according to the deflection by the deflection unit. This prior art apparatus realizes not only the maximum patterning speed of about 5000 patterns per square centimeter but also realizes a minimum size length of less than 1 micron.
However, there is a problem in the above mentioned prior art. That is, although the positions of the first and the second apertures are strictly adjusted to desired positions, they may be deviated from the originally set positions during the passage of time due to, for example, heat produced in the inside of the apparatus by the exposed electron beam. Accordingly, to ensure that the beam size is varied to a size as designed on the surface of the wafer, it is necessary to periodically correct the position of the beam image of the first aperture with respect to the position of the second aperture.